front: Fix scaling for Mayflash N64/USB adapter.

Closes Issue #188 and forum post
http://www.paulscode.com/forum/index.php?topic=1076

Also cleaned up some of the raphnet stuff a little more, trying to
consolidate code.  I'll probably make a sensitivity setting soon to
allow users to compensate for "wear" in the original N64 optical en-
coders.